This invention is directed to an improved method and apparatus for practicing the method by which certain parameters of a staple length distribution of fibers in a yarn sliver can be determined, such as average effective staple length, coefficient of variation of fiber lengths, index of length uniformity, span lengths, and any other well-known statistical parameter of a fiber length distribution.
Both the average filament length and the range of filament lengths, for instance, are important parameters in the processing of staple yarns. Filament lengths are especially important during the sliver drafting operations by fiber processors. If a sliver yarn should contain filaments longer than the distance between the nips of drafting roll pairs in a fiber processing plant, the gap between the drafting roll pairs will be bridged and result in defects known as cockled yarn and tied filaments. Conversely, if the filaments should be too short, the drafted yarn will have thick and thin places resulting in lower uniformity (i.e., high Uster percentage coefficient of variation).
The term "staple length" has taken on many meanings in the textile industry. "True staple length" is commonly referred to as the average filament length after all crimp has been removed from the filaments. "Effective staple length", as will be referred to herein, is the filament length with most of the crimp still in the filaments. Obviously, for a crimped fiber, the effective staple length must always be less than the true staple length.
An object of the present invention, therefore, is to provide a method and an apparatus for practice of the method by which, for example, measurements of the effective staple length can be made under dynamic conditions; "dynamic conditions" being here those conditions encountered in the drafting of yarn slivers by a fiber processor who, upon knowing average "effective staple length", will be able to choose which yarn he will run on which position or to change the distance settings between drafting roll pairs to suit the particular effective staple length.
In the prior art there are at present two methods commonly used to measure "staple length" or at least some parameter related to the staple length. The first of these methods is the "hand array". This method involves manually removing a certain number of single filaments, pulling the crimp from each filament by using tweezers, and carefully measuring the length of each filament with a ruler. The individual values are then averaged. Obviously, this method is very time consuming. Also, due to the necessarily small number of filaments measured, it is difficult to obtain a statistically significant sample. Further, the length parameter, which determines processability of the fiber, is not the actual filament length but rather the effective staple length, the parameter which can be measured by the present invention. Thus, if the crimp level and/or cohesion forces change significantly, the effective staple length can change although the true staple length remains the same.
The second method commonly used to measure staple length is by means of the Fibrograph (See Spinlab Corp., "Measures of Fiber Length -- The Fibrogram Method", Information Bulletin 103, October, 1975). The Fibrograph is an instrument used to measure "fiber extension distances (spun lengths) of fibers in the test specimen". The test specimen used in the Fibrograph is a "beard" of fibers formed by clamping and firmly holding in place the fibers of a cross-section or sliver, roving, etc. After all the loose fibers have been combed from the beard, a light source-photocell scan is made along the length of the beard. The resulting transmitted light intensity versus distance along the beard yields a "fibrogram" similar in shape to that obtained with the present invention. The fiber length parameter measured with the Fibrograph is the "span length", which is defined as the distance from the test specimen clamp line to a point where only a certain percentage of the clamped fibers extend.
There are at least three distinct differences that may be observed between the Fibrograph method and the present invention. First, the Fibrograph looks at only a single cross-section of a sliver per test. The present invention, on the other hand, measures the average staple length along a length (typically 3 feet) of yarn sliver. Second, the Fibrograph measures fiber length properties while the fibers are in a combed-out but relaxed condition. The present invention, on the other hand, measures the fiber length properties under dynamic conditions, as previously mentioned, in which both crimp permanency and cohesive forces interact to influence the effective staple length. Third, the length parameters as measured by each method are different. The present invention measures the average effective staple length, while the Model 430 Fibrograph, for instance, measures the distance (span length) from the test specimen clamp to a point where only a certain percentage of the clamped fibers extend. The Model 430 Fibrograph does have an optional X-Y recorder output with which an average staple length measurement can be made similar to the present invention. However, as noted above, the staple length is measured by the Fibrograph while the filaments are in a relaxed condition, which is not the same as the dynamic conditions under which the yarn would be drafted by a fiber processor.
In the November, 1974, Textile Research Journal, Volume 44, pages 852-855, there is an article entitled "Measurement of Sliver Drafting Forces" by J. S. Olsen of Fiber Surface Research Section, Textile Fibers Department, E. I. du Pont de Nemours and Company, Inc., Kinston, North Carolina, 28501, U.S.A. In this article an apparatus was disclosed by which drafting forces could be measured by using a sensitive watt-meter transducer to measure the power demand of the drafting roll motor. The wattmeter is placed in series with the drafting roll motor electrical supply, since power is a function of force at a fixed roll speed, then wattage becomes a direct measure of drafting force. By use of the disclosure in this Journal article, and modified in the manner disclosed herein, the inventors of the present invention have discovered a number of other parameters can be determined.
Another object of the invention, therefore, is to provide an improved method and apparatus for practicing the method by which parameters of staple length distribution of fibers in a yarn sliver can be readily determined in a relatively short time, as compared to the hand array method, and can also be determined under dynamic conditions as compared to the conditions under the Fibrograph method.